1. Field of the Invention
The field of art to which the claimed invention pertains is catalytic composites particularly useful in the treatment of sour petroleum distillates or fractions, the treatment being commonly referred to as sweetening. More specifically, the claimed invention relates to catalytic composites prepared by sequentially contacting a solid adsorptive support with first a metal chelate solution and thereafter, at an elevated temperature, a substituted ammonium compound.
2. Description of the Prior Art
Processes for the treatment of a sour petroleum distillate, wherein said distillate is passed in contact with a supported metal phthalocyanine catalyst disposed as a fixed bed in a treating or reaction zone, have become well known and widely accepted in the industry. The treating process is typically designed to effect the catalytic oxidation of offensive mercaptans contained in the sour petroleum distillate with the formation of innocuous disulfides. The oxidizing agent is most often air admixed with the sour petroleum distillate to be treated. Gasoline, including natural, straight run and cracked gasolines, is the most frequently treated sour petroleum distillate. Other sour petroleum distillates include the normally gaseous petroleum fraction as well as naphtha, kerosine, jet fuel, fuel oil, lube oil, and the like.
In the manufacture of a supported metal phthalocyanine catalyst, it is the practice to adsorb the metal phthalocyanine on an adsorptive support from a solution and/or dispersion thereof. Alcoholic solutions and/or dispersions, and in particular methanolic solutions, have provided an active catalyst composite, and alcoholic solutions and/or dispersions are commonly employed in the preparation of supported metal phthalocyanine catalysts used throughout the industry in the sweetening of sour petroleum distillates. Aqueous solutions also have been used, but heretofore such solutions have afforded a relatively poor distribution of the metal phthalocyanine on the adsorptive support, and quality control is difficult to achieve. The result has been a catalyst composite of lower activity.
The prior art suggests two ways to improve the oxidation of mercaptans contained in sour petroleum distillates. One way is by increasing the activity of the catalyst by the addition of specified additives to the metal phthalocyanine solutions employed in preparing the catalytic composites. The prior art suggests that to increase the activity of catalytic composites produced with aqueous solutions a strong base, such as ammonia or ammonium hydroxide, be included in the solution (U.S. Pat. No. 3,108,081). The base apparently improves the solubility of the metal phthalocyanine. The prior art also discloses that a higher activity catalytic composite results from the use of a soluble acid amide instead of a strong base (U.S. Pat. No. 4,098,681). A catalytic composite of improved activity has also been found to result from the inclusion of a carboxylic acid in a metal phthalocyanine solution of water (U.S. Pat. No. 4,087,378) or an alcohol (U.S. Pat. No. 4,107,078). Other additives to the metal phthalocyanine solution which have been disclosed as providing a catalytic composite of higher activity are polynuclear aromatic sulfonic acid (U.S. Pat. No. 4,124,531) and morpholine (U.S. Pat. No. 4,142,964 ).
Alternatively to the modification of the metal phthalocyanine catalytic composite by the inclusion with the metal phthalocyanine solution of the additives identified above, the prior art discloses that the improved oxidation of mercaptans contained in some petroleum distillates can be effected by use of additives in the distillate treating process. U.S. Pat. No. 4,124,493 discloses a process for treating a mercaptan-containing sour petroleum distillate, and in particular a distillate boiling at a temperature in excess of 135.degree. C., which comprises contacting said distillate with a supported mercaptan oxidation catalyst at oxidation conditions in the presence of an alkaline reagent and a specified substituted ammonium halide. Metal phthalocyanines were disclosed as a preferred class of mercaptan oxidation catalyst.
Thus, the prior art discloses that additives may be added to the catalyst precursors in the production of the catalyst, or, alternatively, that additives may be added to the distillate to be treated with the catalyst. In either method considerable molar excess of the additive must be used to produce a stable catalyst or to effectively treat the distillate. However, it is generally desired to minimize the amount of additive in the treated distillate, since additives can degrade the quality of the distillate.